The present invention relates to an actuator device, particularly suitable for use in a variable valve apparatus of an internal combustion engine.
A variable valve apparatus is commonly used in an internal combustion engine to vary the operating characteristics such as valve lift amounts of engine valves. Japanese Laid-Open Patent Publication No. 2005-330942 discloses one such type of variable valve apparatus that varies the valve lift amounts of engine intake valves. This variable valve apparatus includes a support pipe (rocker shaft) mounted by journals on a cylinder block of the engine, a drive shaft (control shaft) slidably inserted in the support pipe, an arm assembly disposed on an outer peripheral surface of the support pipe and provided with an input arm, an oscillation cam and a slider gear unit per engine cylinder and an actuator device for moving the drive shaft axially so as to move the slider gear unit in an axial direction of the drive shaft, change a relative phase difference between the input arm and the oscillation cam and thereby control the valve lift amount of the engine valve. In Japanese Laid-Open Patent Publication No. 2005-330942, the actuator device has an electric motor and a ball screw mechanism with a screw shaft and a ball nut so that, when the ball nut rotates upon energization of the electric motor, the ball screw mechanism converts the rotation of the ball screw nut to an axial movement of the screw shaft and transmits the axial movement to the drive shaft.